1. Field of the Invention
The present invention relates generally to a zoom lens system, and more particularly to a wide-field-angle zoom lens system suitable for use on video cameras.
2. Related Art
In recent years, zoom lens systems of the type which, as typically disclosed in JP-A-63-29718, comprise four lens groups or positive, negative, positive, and positive lens groups as viewed from the object side, and in which zooming is carried out by the second group, and correction of an image position due to zooming, and focusing are performed by the fourth group, have prevailed for use on general-purpose video cameras. Most of these types of zoom lens systems are designed to have a field angle 2.omega. of about 50.degree. at the wide-angle end. JP-A-6-94997, on the other hand, discloses a four-group zoom lens system having a field angle as large as about 65.degree. at the wide-angle end. This zoom lens system, comprising positive, negative, positive, and positive lens groups from the object side, achieves a wide field angle by conforming to various conditions while the second, third, and fourth lens groups are movable for zooming. JP-A-6-194572, too, discloses a system having such similar structure as set forth in JP-A-6-94997.
However, the system set forth in JP-A-6-94997 is disadvantageous in terms of cost because its lens barrel becomes large and heavy due to the first lens group that does not only have the largest outer diameter but is constructed of three lenses as well.
JP-A-6- 194572, on the other hand, appears to fail to achieve a wide field angle, because all examples but the fifth one are directed to systems in which the first lens group is constructed of three lenses, and the focal length thereof at the wide-angle end is 5.7 to 6.2 with respect to an image height Y' of 3.1, or the angle of field is of the order of 57 to 53.degree.. The fifth example is directed to a zoom lens system which has an angle of field of about 50.degree. and so is not improved at all in this regard. This is because although the first lens group is constructed of two lenses yet the focal length thereof at the wide-angle end is 6.7 with respect to an image height Y' of 3.1.